Radiative and Photochemical Processes in Mesospheric Dynamics: Part II, Vertical Propagation of Long Period Disturbances at the Equator

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  • 1 Harvard University, Cambridge, Mass.
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Abstract

This paper considers the vertical propagation of a long-period, small-amplitude perturbation in a medium in which radiative transfer and photochemistry play important roles. The perturbation and the basic field are assumed to be axially symmetric and symmetric about the equator; the basic wind field is geostrophic and the basic temperature field is in radiative equilibrium.

It is found that long-period perturbations can only propagate by virtue of the physical effects of radiative transfer and photochemistry. The computed wave propagates downwards and, for a period of 2.2 years, the phase speed is close to the observed speed of 1.5 km month−1 for the “26-month” equatorial oscillation. The observed relative phases of velocity and temperature fields, and the sharp attenuation of the oscillation below 20 to 25 km are also found in the model wave.

There are discrepancies between the model and the observed “26-month” oscillation, which are to be expected in view of the nonlinearity of the observed phenomenon. However, it appears that, for complex reasons, the observed wave may satisfy equations similar to those occurring in the linear theory.

Abstract

This paper considers the vertical propagation of a long-period, small-amplitude perturbation in a medium in which radiative transfer and photochemistry play important roles. The perturbation and the basic field are assumed to be axially symmetric and symmetric about the equator; the basic wind field is geostrophic and the basic temperature field is in radiative equilibrium.

It is found that long-period perturbations can only propagate by virtue of the physical effects of radiative transfer and photochemistry. The computed wave propagates downwards and, for a period of 2.2 years, the phase speed is close to the observed speed of 1.5 km month−1 for the “26-month” equatorial oscillation. The observed relative phases of velocity and temperature fields, and the sharp attenuation of the oscillation below 20 to 25 km are also found in the model wave.

There are discrepancies between the model and the observed “26-month” oscillation, which are to be expected in view of the nonlinearity of the observed phenomenon. However, it appears that, for complex reasons, the observed wave may satisfy equations similar to those occurring in the linear theory.

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